As spring turned to summer this week, extreme heat caught much of New York City by surprise, sending concerned residents to prepare for rising temperatures earlier than usual, while various city agencies, civic organizations and businesses have also been adjusting their seasonal calendars.

As climate change extends the traditional summer and batters the city with spontaneous rain storms, many New Yorkers are discovering that they are not quite in sync with the weather anymore and have to rethink how to adapt to the passing months.

Look no further than this week: The city has already activated its first heat emergency plan of the year, but school remains in session, pools have yet to open and public beaches are still staffing up with lifeguards.

For the most part, New Yorkers made modest adjustments to their schedules, postponing outings or being cautious if they pressed ahead, exercising and running errands, for example, during the morning and the evening — the coolest parts of the day.

“There’s always some natural variability in weather and climate, but climate change is loading the dice so that the calendars we relied on in the past are becoming a losing proposition,” said Radley Horton, a professor at Columbia University’s Climate School.